EP4596955A1

EP4596955A1 - Optical member and illumination device

Info

Publication number: EP4596955A1
Application number: EP23872136.9A
Authority: EP
Inventors: Taichi Watanabe; Kozo Nakamura
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2022-09-29
Filing date: 2023-09-22
Publication date: 2025-08-06
Also published as: KR20250078444A; WO2024070910A1; JP2024049628A; CN119907896A

Abstract

An optical member (100) comprises a light guide member (110) and at least one cover member (200F), (200R), and is configured so as to emit light towards the front surface side. The light guide member comprises: a light guide layer (10) having a light-receiving side surface that receives light emitted from a light source (LS); and a light distribution control structure (14A) that can guide at least a portion of the light propagated inside the light guide layer towards the front surface side. The at least one cover member includes: a first cover member (200F) disposed on the front surface side of the light guide member; or a second cover member (200R) disposed on the rear surface side opposite to the front surface side of the light guide member. The optical member is configured such that over 50% of the light that has entered the light guide layer is emitted from the front surface side of the light guide member.

Description

TECHNICAL FIELD

The present invention relates to an optical member including a light guide layer, and an illumination device including a light source and such an optical member.

BACKGROUND ART

Today, various types of illumination devices using LED elements as light sources are developed. One of such illumination devices is a sheet-like (encompassing plate-like and film-like) illumination device including a light source and a light guide layer.
For example, Patent Document No. 1 discloses an illumination device including a light guide plate installed on a skylight and capable of transmitting sunlight.
Patent Document No. 2 discloses an illumination device including a light guide layer disposed between two cover members. The two cover members are different in the reflectance, so that the output efficiency of light to one side may be improved.

CITATION LIST

PATENT LITERATURE

Patent Document No. 1: Japanese Laid-Open Patent Publication No. 2012-49050
Patent Document No. 2: Japanese Laid-Open Patent Publication No. 2014-10919

SUMMARY OF INVENTION

TECHNICAL PROBLEM

However, the conventional sheet-like illumination devices each including a light source and a light guide layer have various problems and are limited in the application of use.
For example, the illumination device described in Patent Document No. 1 is usable on a skylight, but cannot be installed easily on a window or a wall. In addition, this illumination device has problems, for example, that the utilization factor of light is low and/or that the illumination light is diffused light and thus is clouded (having a large Haze value) when being used for a window. The illumination device described in Patent Document No. 2 uses the reflection by the cover member, and therefore, has a problem that the utilization factor of light transmitted through the illumination device is lowered.
The present invention, made in light of the above-described problems, has an object of providing an illumination device usable for various applications including windows and walls, and an optical member usable for such an illumination device.

SOLUTION TO PROBLEM

Embodiments of the present invention provide the solutions described in the following items.

[Item 1]

An optical member, comprising a light guide member, and at least one cover member, the optical member being configured to output light forward,

wherein the light guide member includes:
- a light guide layer having a light receiving surface at which the light output from a light source is received, and
- a luminous intensity distribution control structure capable of directing, at least forward, a portion of the light propagated in the light guide layer,
wherein the at least one cover member includes a first cover member disposed forward of the light guide member or a second cover member disposed opposite thereto, that is rearward of the light guide member, and
more than 50% of the light incident on the light guide layer is output forward from the light guide member.

[Item 2]

The optical member of item 1, wherein the first cover member and the second cover member each have a reflectance of 25% or lower for visible light incident perpendicularly thereon from the side of the light guide layer.

[Item 3]

The optical member of item 1 or 2, wherein the first cover member or the second cover member includes a glass plate.

[Item 4]

The optical member of item 3, wherein the first cover member further includes a reflection-preventive layer provided on at least one main surface of the glass plate.

[Item 5]

The optical member of any one of items 1 through 4, wherein where a light beam having a highest luminous intensity in a luminous intensity distribution of light output forward from the light guide member is a first main light beam and a light beam having a highest luminous intensity in a luminous intensity distribution of light output rearward from the light guide member is a second main light beam, a polar angle θ1 of the first main light beam with respect to the normal to the light guide layer is smaller than a polar angle θ2 of the second main light beam with respect to the normal to the light guide layer.

[Item 6]

The optical member of item 5, wherein where the polar angle θ1 is 0° or larger and smaller than 40°, and the polar angle θ2 is 30° or larger and smaller than 70°.

[Item 7]

The optical member of any of items 1 through 6, wherein the light guide member and the at least one cover member are disposed to be away from each while having a gas layer therebetween.

[Item 8]

The optical member of any of items 1 through 7, wherein the light guide layer is formed of an acrylic resin.

[Item 9]

The optical member of any of items 1 through 8, wherein the luminous intensity distribution control structure includes a plurality of internal spaces each having a forward inclining surface directing light forward by total internal reflection.

[Item 10]

The optical member of any of items 1 through 9, wherein the luminous intensity distribution control structure is formed in a direction conversion layer disposed forward or rearward of the light guide layer.

[Item 11]

The optical member of any of items 1 through 10, wherein the light guide member has a visible light transmittance of 60% or higher and a Haze value of smaller than 10%.

[Item 12]

An illumination device, comprising:

the optical member of any of items 1 through 11; and
a light source disposed so as to output light toward the light receiving surface of the optical member.

ADVANTAGEOUS EFFECTS OF INVENTION

Embodiments of the present invention provide an illumination device usable for various applications including windows and walls, and an optical member usable for such an illumination device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an illumination device 1000 according to an embodiment of the present invention.
FIG. 2 is a schematic plan view of a light guide member 110 included in the illumination device 1000.
FIG. 3A is a schematic cross-sectional view of an internal space 14A that may be included in the light guide member 110.
FIG. 3B is a schematic plan view of the internal space 14A.
FIG. 3C is a schematic plan view showing a variation of the internal space 14A.
FIG. 4 is a schematic cross-sectional view of a light guide member 110A included in an illumination device according to another embodiment of the present invention.
FIG. 5 is a schematic cross-sectional view of a light guide member 110B included in an illumination device according to still another embodiment of the present invention.
FIG. 6 is a schematic partial perspective view of an optical member 300A according to an embodiment of the present invention.
FIG. 7 is a schematic partial perspective view of an optical member 300B according to an embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, optical members and illumination devices according to embodiments of the present invention will be described with reference to the drawings. The optical members and the illumination devices according to embodiments of the present invention are not limited those described below.
FIG. 1 is a schematic cross-sectional view of an illumination device 1000 according to an embodiment of the present invention. In the figure, dashed arrows represent examples of light beams.
The illumination device 1000 includes a light source LS and an optical member 100. The optical member 100 includes a light guide member 110, a first cover member 200F, and a second cover member 200R, and is configured to output light forward (in FIG. 1 , in a -Z direction).
The light guide member 110 includes a light guide layer 10 having a light receiving surface at which the light output from the light source LS is received, and a luminous intensity distribution control structure capable of directing, at least forward, a portion of the light propagated in the light guide layer 10 (y direction). The luminous intensity distribution control structure provided herein as an example includes a plurality of internal spaces 14A each having a forward inclining surface ISa directing the light forward by total internal reflection (TIR). The "forward" of the "forward inclining surface" of each internal space refers to that the forward inclining surface, among inclining surfaces of the internal space, is on a light receiving side (closer to the light receiving surface). Among the inclining surfaces of each internal space, an inclining surface disposed opposite to the light receiving surface (farther from the light receiving surface) will be referred to as a "rearward inclining surface").
The light guide member 110 includes the luminous intensity distribution control structure in the light guide layer 10. The present invention is not limited to this. As described below as an example, the light guide member may further include a direction conversion layer (may also be referred to as a "light retrieval layer"), and the direction conversion layer may include the luminous intensity distribution control structure. The light guide member 110 is configured such that more than 50% of the light incident on the light guide layer 10 is output forward from the light guide member 110.
The optical member 100 includes a first cover member 200F disposed forward of the light guide member 110 and a second cover member 200R disposed opposite thereto, that is, rearward of the light guide member 110. One of the first cover member 200F and the second cover member 200R may be omitted. The first cover member 200F or the second cover member 200R may be disposed on the side where the light guide member 110 is to be protected, in accordance with the environment in which the illumination device 1000 is used.
The first cover member 200F and the second cover member 200R are disposed to be away from each other while having the light guide member 110 and a gas layer GL therebetween. The gas layer GL may be, for example, an air layer. For example, a sealed space may be formed between the first cover member 200F and the light guide member 110 and/or between the second cover member 200R and the light guide member 110, like in a multiple glazing glass plate having a high thermal insulation performance, and the glass layer GL may be formed of, for example, argon gas. In the case where such a multiple glazing glass plate is formed, a spacer including a desiccant may be further disposed so as to be in contact with the gas layer GL.
In the case where the gas layer GL is provided, the total reflection at an interface between the light guide member 110 and the gas layer GL may be used to propagate the light efficiently in the light guide member 110. Instead of the gas layer GL, a low refractive index layer (e.g., having a refractive index of 1.30 or lower) may be provided. The light guide member 110 and the first cover member 200F and/or the second cover member 200R may be bonded together with, for example, a pressure-sensitive adhesive layer. In this case, it is preferred that no optical interface is formed between the light guide member 110, the pressure-sensitive adhesive layer, the first cover member 200F and/or the second cover member 200R.
It is preferred that the first cover member 200F and the second cover member 200R each have a reflectance of 25% or lower for visible light incident thereon vertically from the side of the light guide member 110. For example, Low-E glass may be used for the first cover member 200F and/or the second cover member 200R. The Low-E (low emissivity) glass includes a Low-E metal (e.g., silver) film (and a metal oxide film) on a surface of the glass plate. The Low-E metal is disposed on a surface of the glass plate that is closer to the light guide member 110.
The first cover member 200F and/or the second cover member 200R may include a glass plate. The first cover member 200F and/or the second cover member 200R may include a plastic plate having a high visible light transmittance. As the plastic material, polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinylchloride (PVC), or polyethyleneterephthalate (PET) is usable, for example. Note that a glass plate has properties of, for example, having a higher hardness and having a higher flame retardancy than those of a plastic plate. Therefore, it is preferred to use a glass plate as a component for construction. By contrast, for a window of a showcase or the like, it is preferred to use a plastic plate, which is lightweight. There is no limitation on the thickness of the glass plate or the plastic plate. The thickness of the glass plate or the plastic plate may be appropriately set in accordance with the use thereof, with no specific limitation. The thickness of the glass plate is, for example, 1 mm or greater and 15 mm or less. The thickness of the plastic plate is, for example, 1 mm or greater and 15 mm or less.
For a use for which thermal shielding performance or thermal insulation performance is required, the Low-E glass mentioned above is preferably used. It is preferred that the first cover member 200F and the second cover member 200R have a high visible light transmittance and a low visible light reflectance. The visible light reflectance of each of the first cover member 200F and the second cover member 200R is preferably 15% or lower, more preferably 10% or lower, still more preferably 5% or lower, and still more preferably 3% or lower. The first cover member 200F and/or the second cover member 200R having such a low visible light reflectance may be provided by provision of a reflection-preventive film on at least one main surface of a glass plate or a plastic plate. As the reflection-preventive film, any of various known reflection-preventive films may be used. For example, as described in experiment examples, low reflection film Leclear II produced by Sangetsu Corporation may be bonded to at least one main surface of a glass plate or a plastic plate. For example, a reflection-preventive film is provided on at least one of two main surfaces of the first cover member 200F, which is disposed on the light output side.
As shown in FIG. 1 , the illumination device 1000 outputs light LRf forward and outputs light LRr rearward. The luminous intensity distribution of the light output forward and the luminous intensity distribution of the light output rearward are different from each other. The luminous intensity distribution may be controlled by, for example, adjustment on an inclination angle θa of a forward inclining surface ISa and/or an inclination angle θb of a rearward inclining surface ISb.
The "luminous intensity distribution" of an illumination device refers to the distribution of the luminous intensity (strength) with respect to the angle, and does not depend on the wavelength of the light output from the illumination device. The luminous intensity distribution of an illumination device is measured by a method conformed to, for example, JIS C8105-5. The luminous intensity distribution is characterized by, for example, a direction of a light beam having the highest luminous intensity (intensity) (hereinafter, referred to as the "main light beam").
Where the light beam having the highest strength in the luminous intensity distribution of the light output forward from the light guide member 110 is a first main light beam and the light beam having the highest strength in the luminous intensity distribution of the light output rearward from the light guide member 110 is a second main light beam, a polar angle θ1 of the first main light beam with respect to the normal to the light guide layer 10 is smaller than a polar angle θ2 of the second main light beam with respect to the normal to the light guide layer 10. For example, the polar angle θ1 is 0° or larger and smaller than 40°, and the polar angle θ2 is 30° or larger and smaller than 70° (see, for example, Japanese Patent Application No. 2021-096846 ). The entirety of the disclosure of Japanese Patent Application No. 2021-096846 is incorporated therein by reference. The light guide member 110 has such a luminous intensity distribution, so that the illumination device 1000 may output a larger amount of light forward than rearward. That is, the light guide member 110 is configured such that more than 50% of the light incident on the light guide layer 10 is output forward from the light guide member 110. The illumination device 1000 is capable of outputting light having a high directivity forward.
The light guide member 110 has a visible light transmittance of, for example, 60% or higher. The light guide member 110 has a Haze value of, for example, smaller than 10%. The visible light transmittance of the light guide member 110 is preferably 70% or higher, and more preferably 80% or higher. The Haze value of the light guide member 110 is preferably 5% or smaller. Herein, the visible light is defined as light having a wavelength of 380 nm or longer and 780 nm or shorter. The visible light transmittance and the Haze value may be measured by use of, for example, a Haze meter (trade name: HM-150; produced by Murakami Color Research Laboratory Co., Ltd.).
The light source LS is, for example, an LED device. An array of a plurality of LED devices may be used as the light source LS. Alternatively, a coupling optical system may be provided between the light source LS and the light guide layer 10 to guide the light output from the light source LS to the light guide layer 10 efficiently.
The luminous intensity distribution may be controlled by, for example, adjustment on the cross-sectional shape, the planar shape, the size, the density in the light guide layer 10, and the distribution of the internal spaces 14A. As described below with reference to FIG. 3A , the inclination angle θa of the forward inclining surface ISa is, for example, 10° or larger and 70° or smaller. The inclination angle θb of the rearward inclining surface ISb is, for example, 50° or larger and 100° or smaller. Herein, the cross-sectional shape of the internal spaces 14A is triangular. The present invention is not limited to this, and the cross-sectional shapes of the internal spaces 14A may be independent from each other and may be trapezoidal or the like.
Regarding the plurality of internal spaces 14A, which are provided as the luminous intensity distribution control structure, as seen in the direction of the normal to a main surface of the light guide layer 10, the ratio of the area size of the plurality of internal spaces 14A with respect to the area size of the light guide layer 10 (occupancy area ratio) is preferably 1% or higher and 80% or lower. The upper limit of the occupancy area ratio is preferably 50%, and more preferably 45%. In order to provide a high transmittance and/or a low Haze value, the upper limit of the occupancy area ratio is preferably 30%, more preferably 10%, and still more preferably 5%. When, for example, the occupancy area ratio of the internal spaces is 50%, a Haze of 30% may be provided. The occupancy area ratio of the internal spaces 14A may be uniform, or may be increased as the distance from the light source LS is increased such that the luminance is not decreased even as the distance from the light source LS is increased. In order to mass-produce the luminous intensity distribution control structure by a roll-to-roll method or a roll-to-sheet method, it is preferred that the occupancy area ratio of the internal spaces 14A is uniform.
Now, with reference to FIG. 2 , an example of planar shape and positional arrangement of the internal spaces 14A will be described. FIG. 2 is a schematic plan view of the light guide member 110. With reference to FIG. 3A, FIG. 3B and FIG. 3C , the shape of the internal spaces 14A will be described. FIG. 3A is a schematic cross-sectional view of the internal space 14A. FIG. 3B is a schematic plan view of the internal space 14A. FIG. 3C is a schematic plan view showing a variation of the internal space 14A.
As shown in FIG. 2 , the plurality of internal spaces 14A are discretely arranged in, for example, a light guide direction of the light guide layer 10 (in a y direction) and in a direction perpendicular to the light guide direction (in an x direction). Regarding the size (length L and width W; see FIG. 3A and FIG. 3B ) of the internal space 14A, the length L is preferably 10 µm or longer and 500 µm or shorter, and the width W is preferably 1 µm or longer and 100 µm or shorter, for example. From the point of view of the light retrieval efficiency, the height H (see FIG. 3A ) is preferably 1 µm or longer and 100 µm or shorter.
Herein, an example in which the plurality of internal spaces 14A are discretely arranged in the light guide direction of the light guide layer 10 (in the y direction) and in the direction perpendicular to the light guide direction (in the x direction) is described. The present invention is not limited to this, and the plurality of internal spaces 14A may be discretely arranged in the light guide direction of the light guide layer 10 (in the y direction) and a direction crossing the light guide direction. The discrete positional arrangement of the internal spaces 14A may be appropriately set in accordance with the shape of the light guide layer 10, the required luminous intensity distribution, or the like. In the light guide layer 10, the light is propagated in various directions. The y direction will be referred to as the "light guide direction", and light having a component of the y direction (not zero) will be expressed as "being propagated in the y direction". The same is applicable to the other directions. That is, light propagated in a -y direction encompasses all the light having a component of the -y direction (not zero).
The plurality of internal spaces 14A are discretely arranged in, for example, the light guide direction and a direction crossing the light guide direction. The discrete positional arrangement may be periodical (regular) in at least one direction, or may not be periodical. Note that it is preferred that the plurality of internal spaces 14A are arranged uniformly from the point of view of the mass-productivity. For instance, in the example shown in FIG. 2 , the plurality of internal spaces 14A having substantially the same shape and having curved surfaces protruding in substantially the same direction are arranged in the light guide direction of the light guide layer 10 (in the y direction) and in the direction perpendicular to the light guide direction (in the x direction), discretely and periodically in the entirety of the region. In this case, a pitch Px is preferably, for example, 10 µm or longer and 500 µm or shorter, and a pitch Py is preferably, for example, 10 µm or longer and 500 µm or shorter. In the example shown in FIG. 2 , there are also internal spaces shifted from the above-described internal spaces 14A by a 1/2 pitch in each of the y direction and the x direction.
As shown in FIG. 2 , as seen from the direction of the normal to the main surface of the light guide layer 10, the forward inclining surfaces ISa each form a curve protruding toward the light source LS. The light source LS includes, for example, an LED device. A plurality of LEDs are arranged in the x direction. Light that is output from each of the plurality of LEDs expands with respect to the y direction. Therefore, each of the forward inclining surfaces ISa, in the case of having a curve protruding toward the light source LS, acts uniformly on the light. In the case where a coupling optical system is provided between the light source LS and the light receiving surface of the light guide member 110 to cause light having a high degree of parallelism (light not largely expanding with respect to the y direction) to be incident, the forward inclining surfaces ISa may be parallel to the x direction. Instead of the internal spaces 14A discretely arranged, internal spaces like grooves extending in the x direction (e.g., triangular prisms) may be provided, for example.
As shown in FIG. 3A , the internal spaces 14A each have, for example, a triangular cross-section. The inclination angle θa of the forward inclining surface ISa, which is closer to the light source LS, is, for example, 10° is larger and 70° or smaller. In the case where the inclination angle θa is smaller than 10°, the controllability on the luminous intensity distribution is decreased, and also the light retrieval efficiency may possibly be decreased. By contrast, in the case where the inclination angle θa exceeds 70°, the production of the luminous intensity distribution control structure may possibly be difficult, for example. The inclination angle θb of the rearward inclining surface ISb is, for example, 50° or larger and 100° or smaller. In the case where the inclination angle θb is smaller than 50°, stray light may possibly be generated in a direction not intended. By contrast, in the case where the inclination angle θb exceeds 100°, the production of the luminous intensity distribution control structure may possibly be difficult, for example. As shown in FIG. 3B and FIG. 3C , the length L of each internal space 14A is preferably 10 µm or longer and 500 µm or shorter, and the width W of each internal space 14A is preferably 1 µm or longer and 100 µm or shorter. The length L is, for example, at least twice the width W. The height H (see FIG. 3A ) is preferably 1 µm or longer and 100 µm or shorter. A recessed portion having a planar shape shown in FIG. 3B is to be formed, but in the case where the formation of the recessed portion is performed at a certain processing precision, a recessed portion having a planar shape shown in FIG. 3C may possibly be formed. Even in such a case, the planar shape of the internal space may be characterized by the length L and the width W. The shape of the curve, protruding toward the light source LS, of the forward inclining surface ISa, as seen from the direction of the normal to the main surface of the light guide layer 10, may be represented by, for example, a biquadratic curve. The internal spaces 14A may be formed of, for example, a shape-forming film having recessed portions at a surface thereof and an adhesive layer, as described below.
Now, with reference to FIG. 4 and FIG. 5 , illumination devices according to other embodiments of the present invention will be described. In each of the illumination devices described below as examples, the luminous intensity distribution control structure is formed in a direction conversion layer disposed forward or rearward of the light guide layer.
FIG. 4 is a schematic cross-sectional view of a light guide member 110A included in an illumination device according to another embodiment of the present invention. FIG. 4 also shows the light source LS.
The light guide member 110A includes a light guide layer 10A having a light receiving surface at which light output from the light source LS is received, and a direction conversion layer 60A disposed rearward of the light guide layer 10A with an adhesive layer 52 being disposed between the direction conversion layer 60A and the light guide layer 10A. The direction conversion layer 60A includes a luminous intensity distribution control structure capable of directing, at least forward, a portion of light propagated in the light guide layer 10A (y direction). The luminous intensity distribution control structure provided herein as an example includes a plurality of internal spaces 64A each having a forward inclining surface directing the light forward by total internal reflection. The direction conversion layer 60A including the plurality of internal spaces 64A includes a shape-forming film 64, having recessed portions 64A (represented by the same reference sign as that of the internal spaces 64A) at a surface thereof, and an adhesive layer 54. The adhesive layer 54 bonds the shape-forming film 64 and a substrate layer 30 to each other.
FIG. 5 is a schematic cross-sectional view of a light guide member 110B included in an illumination device according to still another embodiment of the present invention. FIG. 5 also shows the light source LS.
The light guide member 110B includes a light guide layer 10B having a light receiving surface at which light output from the light source LS is received, and a direction conversion layer 60B disposed forward of the light guide layer 10B. The direction conversion layer 60B includes a luminous intensity distribution control structure capable of directing, at least forward, a portion of light propagated in the light guide layer 10B (y direction). The luminous intensity distribution control structure provided herein as an example includes a plurality of internal spaces 64A each having a forward inclining surface directing the light forward by total internal reflection. The direction conversion layer 60B including the plurality of internal spaces 64A includes a shape-forming film 64, having recessed portions 64A (represented by the same reference sign as that of the internal spaces 64A) at a surface thereof, and an adhesive layer 54. The adhesive layer 54 bonds the shape-forming film 64 and the light guide layer 10B to each other.
A shape-forming film used to form the internal spaces may be produced as follows, for example. A concaved and convexed shape-forming film was produced in accordance with the method described in PCT Japanese National-Phase Laid-Open Publication No. 2013-524288 . Specifically, a surface of a polymethylmethacrylate (PMMA) film was coated with lacquer (Finecure RM-64 produced by Sanyo Chemical Industries, Ltd.), an optical pattern was embossed on the surface of the film including the lacquer, and then the lacquer was cured. In this manner, an intended concaved and convexed shape-forming film was produced. The shape-forming film has a total thickness of 130 µm.
The light guide layer is formed of a known material having a high visible light transmittance. The light guide layer is formed of, for example, an acrylic resin such as polymethylmethacrylate (PMMA) or the like, a polycarbonate(PC)-based resin, a cycloolefin-based resin, or glass (e.g., quartz glass, alkali-free glass, or borosilicate glass). The light guide layer has a refractive index n_GP of, for example, 1.40 or higher and 1.80 or lower. The "refractive index" refers to a refractive index measured by an ellipsometer at a wavelength of 550 nm, unless otherwise specified. The light guide layer has a thickness that may be appropriately set in accordance with the use thereof. The thickness of the light guide layer is, for example, 0.05 mm or greater and 50 mm or less.
The substrate layer is also used for the light guide layer. The substrate layer is formed of a plastic material having a high visible light transmittance, for example, an acrylic resin such as polymethylmethacrylate (PMMA) or the like, a polycarbonate(PC)-based resin or a cycloolefin-based resin. The substrate layer has a thickness of, for example, 1 µm or greater and 1000 µm or less, preferably 10 µm or greater and 100 µm or less, and more preferably 20 µm or greater and 80 µm or less. The substrate layers each independently have a refractive index of, preferably independently 1.40 or higher and 1.70 or lower, and more preferably independently 1.43 or higher and 1.65 or lower.
The adhesive layers each independently have a thickness of, for example, 0.1 µm or greater and 100 µm or less, preferably 0.3 µm or greater and 100 µm or less, and is more preferably 0.5 µm or greater and 50 µm or less. The adhesive layers each independently have a refractive index of, preferably 1.42 or higher and 1.60 or lower, and more preferably 1.47 or higher and 1.58 or lower. The refractive index of each of the adhesive layers is preferably close to the refractive index of the light guide layer, the shape-forming film or the substrate layer that is in contact with the adhesive layer. It is preferred that an absolute value of the difference in such refractive indices is 0.2 or smaller.
It is preferred that the adhesive layer that is in contact with the recessed portions at the surface of the shape-forming film and defines the internal spaces adheres to the surface of the shape-forming film without burying the recessed portions. As an adhesive preferred to form such an adhesive layer, any of the adhesives described in WO2021/167090 , WO2021/167091 and WO2022/176658 , which are all filed by the present Applicant, are preferably usable. The entirety of the disclosures of these applications are incorporated therein by reference. The polyester-based adhesive described in WO2022/176658 is especially preferred.
In the case where a glass plate is used as the light guide layer 10A of the light guide member 110A, it is merely needed to dispose the second cover member 200R rearward of the light guide member 110A in order to provide an optical member superb in the hardness (strength) and the flame retardancy. In the case where a glass plate is used as the light guide layer 10B of the light guide member 110B, it is merely needed to dispose the first cover member 200F forward of the light guide member 110B in order to provide an optical member superb in the hardness (strength) and the flame retardancy. In either case, the first cover member 200F may be disposed forward of the light guide member 110A or 110B and also the second cover member 200R may be disposed rearward of the light guide member 110A or 110B, needless to say. For a use where at least one of the hardness (strength) and the flame retardancy is not required, the light guide layer 10A or 10B may be formed of a plastic material. In the case where the light guide layer 10A or 10B is formed of a plastic material, it is preferred to use an acrylic resin, which has an especially high visible light transmittance.
Optical members having various configurations were produced experimentally by use of a light guide member having the same configuration as that of the light guide member 100A shown in FIG. 4 (examples 1 through 12, and the comparative example). As each of the first cover member 200F and the second cover member 200R, an acrylic (PMMA) plate or a glass plate was used. An optical member including a reflection-preventive film (AR) provided forward of (outer to) the first cover member 200F and an optical member including a reflection-preventive film (AR) provided forward of (inner to) the second cover member 200R were produced. As the reflection-preventive film, Leclear II produced by Sangetsu Corporation was used. An optical member including neither the first cover member 200F nor the second cover member 200R was produced as the comparative example.
As the light guide member 110A, a light guide member having the parameters shown in Table 1 below was used. As the light guide layer 10, an acrylic plate having a thickness of 5 mm was used. As the substrate layer 30, an acrylic film having a thickness of 30 µm was used. The thickness of the shape-form ing film 64 was 40 µm. As each of the adhesive layers 52 and 54, an acrylic pressure-sensitive adhesive having a thickness of 50 µm was used. The visible light transmittance of the light guide member was 93%, and the Haze value thereof was 3%. The visible light transmittance and the Haze value were measured by use of, for example, a Haze meter (trade name: HM-150; produced by Murakami Color Research Laboratory Co., Ltd.). [Table 1]

Px (µm) Py (µm) W (µm) L (µm) H (µm) θa (°) θb (°) OCCUPANCY AREA RATIO (%)

120 140 14.55 61 8 30 85 6.96

Table 2 below shows the configurations and the properties of the optical members produced experimentally, The reflectance of the surface of the first cover member 200F (front (outer) surface) and the reflectance of the surface of the second cover member 200R (front (inner) surface) were measured by the UV-Vis-NIR spectrophotometer UH4150 with a halogen lamp being used as the light source. As the appearance, the transmittance of the optical member was evaluated by visual inspection. A target such as experiment equipment or the like was visually observed through each of the optical members. An optical member through which the target was seen very clearly with very little glare was evaluated as "very good" (⊚), an optical member through which the target was seen clearly with little glare was evaluated as "good" (○), and an optical member through which the target was seen with slight glare was evaluated as "acceptable" (△). The optical members in the examples each include at least the first cover member 200F or the second cover member 200R, and therefore, are sufficient (○) in the surface protection of the light guide members thereof. The optical members including both of the first cover member 200F and the second cover member 200R are particularly excellent (⊚) in the surface protection of the light guide members thereof. The optical member in the comparative example includes neither the first cover member 200F nor the second cover member 200R, and therefore, is not capable of protecting the surface of the light guide member thereof (×). Regarding the flame retardancy for the use in construction, an optical member in which either one of the first cover member 200F and the second cover member 200R included a glass plate was evaluated as good (○), and an optical member in which both of the first cover member 200F and the second cover member 200R included a glass plate was evaluated as very good (⊚).

[Table 2]

	1ST COVER MEMBER 200F	2ND COVER MEMBER 200R	1ST COVER MEMBER SURFACE REFLECTANCE	2ND COVER MEMBER SURFACE REFLECTANCE	APPEARANCE (TRANSMITTANCE)	SURFACE PROTECTION OF LIGHT GUIDE MEMBER	FRAME RETARDANCY
EX. 1	NONE	GLASS PLATE WITH AR	-	0.9%	⊚	○	○
EX. 2	GLASS PLATE WITH AR	NONE	0.9%	-	⊚	○	○
EX. 3	NONE	ACRYLIC PLATE WITH AR	-	0.9%	⊚	○	×
EX. 4	ACRYLIC PLATE WITH AR	NONE	0.9%	-	⊚	○	×
EX. 5	GLASS PLATE	GLASS PLATE WITH AR	8.5%	0.9%	○	⊚	⊚
EX. 6	GLASS PLATE WITH AR	GLASS PLATE	0.9%	8.5%	○	⊚	⊚
EX. 7	GLASS PLATE WITH AR	GLASS PLATE WITH AR	0.9%	0.9%	⊚	⊚	⊚
EX. 8	ACRYLIC PLATE	ACRYLIC PLATE WITH AR	7.5%	0.9%	○	⊚	×
EX. 9	ACRYLIC PLATE WITH AR	ACRYLIC PLATE	0.9%	7.5%	○	⊚	×
EX. 10	ACRYLIC PLATE WITH AR	ACRYLIC PLATE WITH AR	0.9%	0.9%	⊚	⊚	×
EX. 11	GLASS PLATE	GLASS PLATE	8.5%	8.5%	Δ	⊚	⊚
EX. 12	ACRYLIC PLATE	ACRYLIC PLATE	7.5%	7.5%	Δ	⊚	×
COMPARATIVE EXAMPLE.	NONE	NONE	-	-	⊚	×	×

As described above, the optical member according to an embodiment of the present invention includes a cover member protecting the light guide member and has a high visible light transmittance, and therefore, does not spoil the appearance.
FIG. 6 is a schematic partial perspective view of an optical member 300A according to an embodiment of the present invention. The optical member 300A is, for example, a multiple glazing glass plate. The multiple glazing glass plate 300A includes the light guide member 110A or 110B and the first cover member 200F or the second cover member 200R. The light guide member 110A or 110B and the first cover member 200F or the second cover member 200R are secured to each other while being away from each other by a certain interval by a spacer 80, and define a gas layer GL in the sealed space. The direction in which the light is output (i.e., the forward direction) may be selected in accordance with the orientation in which the light guide member 110A or 110B is disposed. The spacer 80 includes a desiccant therein and removes moisture from the gas of the gas layer GL.
FIG. 7 is a schematic partial perspective view of an optical member 300B according to an embodiment of the present invention. The optical member 300B is, for example, a multiple glazing glass plate. The multiple glazing glass plate 300B includes the light guide member 110A or 110B, the first cover member 200F and the second cover member 200R. The direction in which the light is output (i.e., the forward direction) may be selected in accordance with the orientation in which the light guide member 110A or 110B is disposed. That is, the positions of the first cover member 200F and the second cover member 200R may be exchanged. The light guide member 110A or 110B and each of the first cover member 200F and the second cover member 200R are secured to each other while being away from each other by a certain interval by a spacer 80, and define a gas layer GL in the sealed space.

INDUSTRIAL APPLICABILITY

The illumination device according to the present invention is usable for various applications including windows and walls.

REFERENCE SIGNS LIST

10: light guide layer; 14A: internal space; 100: optical member; 10: light guide member; 200F: first cover member; 200R: second cover member; 1000: illumination device

Claims

An optical member, comprising a light guide member, and at least one cover member, the optical member being configured to output light forward,
wherein the light guide member includes:
a light guide layer having a light receiving surface at which the light output from a light source is received, and

a luminous intensity distribution control structure capable of directing, at least forward, a portion of the light propagated in the light guide layer,

wherein the at least one cover member includes a first cover member disposed forward of the light guide member or a second cover member disposed opposite thereto, that is rearward of the light guide member, and

more than 50% of the light incident on the light guide layer is output forward from the light guide member.
The optical member of claim 1, wherein the first cover member and the second cover member each have a reflectance of 25% or lower for visible light incident perpendicularly thereon from the side of the light guide layer.
The optical member of claim 1, wherein the first cover member or the second cover member includes a glass plate.
The optical member of claim 3, wherein the first cover member further includes a reflection-preventive layer provided on at least one main surface of the glass plate.
The optical member of any one of claims 1 through 4, wherein where a light beam having a highest luminous intensity in a luminous intensity distribution of light output forward from the light guide member is a first main light beam and a light beam having a highest luminous intensity in a luminous intensity distribution of light output rearward from the light guide member is a second main light beam, a polar angle θ1 of the first main light beam with respect to the normal to the light guide layer is smaller than a polar angle θ2 of the second main light beam with respect to the normal to the light guide layer.
The optical member of claim 5, wherein where the polar angle θ1 is 0° or larger and smaller than 40°, and the polar angle θ2 is 30° or larger and smaller than 70°.
The optical member of any one of claims 1 through 4, wherein the light guide member and the at least one cover member are disposed to be away from each while having a gas layer therebetween.
The optical member of any one of claims 1 through 4, wherein the light guide layer is formed of an acrylic resin.
The optical member of any one of claims 1 through 4, wherein the luminous intensity distribution control structure includes a plurality of internal spaces each having a forward inclining surface directing light forward by total internal reflection.
The optical member of any one of claims 1 through 4, wherein the luminous intensity distribution control structure is formed in a direction conversion layer disposed forward or rearward of the light guide layer.
The optical member of any one of claims 1 through 4, wherein the light guide member has a visible light transmittance of 60% or higher and a Haze value of smaller than 10%.
An illumination device, comprising:
the optical member of any one of claims 1 through 4; and

a light source disposed so as to output light toward the light receiving surface of the optical member.